add api for public keys

This enables pkictl to generate public keys from private keys in the rsa
and ecdsa format.

main.go

@@ -13,6 +13,7 @@ const (
   TypeLabelRSA   = "RSA PRIVATE KEY"
   TypeLabelECDSA = "EC PRIVATE KEY"
   TypeLabelCSR   = "CERTIFICATE REQUEST"
+  TypeLabelPubKey = "PUBLIC KEY"
 )
 
 var (
@@ -24,11 +25,13 @@ func main() {
     crash_with_help(1, "No module selected!")
   }
   switch os.Args[1] {
-  case "create-private": create_private_key()
+  case "create-private":   create_private_key()
   case "create-cert-sign": create_sign_request()
+  case "create-public":    create_public_key()
   case "help": print_modules()
   case "info": info_on_file()
-  case "sign": sign_request()
+  case "sign-request": sign_request()
+  case "sign-input":   sign_input()
   default: crash_with_help(1, "Command not supported!")
   }
 }
@@ -37,6 +40,8 @@ func main() {
 func info_on_file() {}
 // sign a certificate request to create a new certificate
 func sign_request() {}
+// sign a message with a private key
+func sign_input() {}
 
 // open stream for given path
 func open_output_stream(path string) (io.WriteCloser, error) {
@@ -57,6 +62,7 @@ func print_modules() {
   fmt.Printf(`Usage: %s command args
 where 'command' is one of:
     create-private    create a new private key
+    create-public     create a public key from a private one
     create-cert-sign  create a new certificate sign request
     help              show this help
     info              get info on a file

private_key.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+  "crypto"
   "crypto/elliptic"
   "crypto/ecdsa"
   "crypto/rand"
@@ -15,7 +16,9 @@ import (
 )
 
 type (
-  PrivateKey interface {}
+  PrivateKey interface {
+    Public() crypto.PublicKey
+  }
 
   CreateFlags struct {
     CryptType   string // rsa or ecdsa

public_key.go

@@ -0,0 +1,46 @@
+package main
+
+import (
+  "crypto/x509"
+  "encoding/pem"
+  "flag"
+  "fmt"
+  "io"
+  "os"
+)
+
+type (
+  PublicKeyFlags struct {
+    PrivateKeyPath string
+    Output         string
+
+    output_stream io.WriteCloser // the actual stream to the output
+  }
+)
+
+func create_public_key() {
+  var err error
+  flags := parse_public_key_flags()
+  flags.output_stream, err = open_output_stream(flags.Output)
+  if err != nil {
+    crash_with_help(2, fmt.Sprintf("Error when creating file %s: %s", flags.Output, err))
+  }
+  priv_key := load_private_key(flags.PrivateKeyPath)
+  marshal, err := x509.MarshalPKIXPublicKey(priv_key.Public())
+  if err != nil {
+    crash_with_help(2, fmt.Sprintf("Problems marshalling the public key: %s", err))
+  }
+
+  block := &pem.Block{Type: TypeLabelPubKey, Bytes: marshal}
+  pem.Encode(flags.output_stream, block)
+}
+
+func parse_public_key_flags() PublicKeyFlags {
+  flags := PublicKeyFlags{}
+  fs := flag.NewFlagSet("create-public", flag.ExitOnError)
+  fs.StringVar(&flags.PrivateKeyPath, "private-key", "", "path to the private key file")
+  fs.StringVar(&flags.Output, "output", "STDOUT", "path where the generated csr should be stored")
+  fs.Parse(os.Args[2:])
+
+  return flags
+}